Comparison of Soil Carbon Dioxide Flux Measurements by Static and Portable Chambers In Various Management Practices.

Portable chamber provides simple, rapid, and inexpensive measurement of soil CO₂ flux but its effectiveness and precision compared with the static chamber in various soil and management practices is little known. Soil CO₂ flux measured by a portable chamber using infrared analyzer was compared with a static chamber using gas chromatograph in various management practices from May to October 2008 in loam soil (Luvisols) in eastern Montana and in sandy loam soil (Kastanozems) in western North Dakota, USA. Management practices include combinations of tillage, cropping sequence, and N fertilization in loam and irrigation, tillage, crop rotation, and N fertilization in sandy loam. It was hypothesized that the portable chamber would measure CO₂ flux similar to that measured by the static chamber, regardless of soil types and management practices. In both soils, CO₂ flux peaked during the summer following substantial precipitation and/or irrigation (>15 mm), regardless of treatments and measurement methods. The flux varied with measurement dates more in the portable than in the static chamber. In loam, CO₂ flux was 14-87% greater in the portable than in the static chamber from July to mid-August but 15-68% greater in the static than in the portable chamber from late August to October in all management practices. In sandy loam, CO₂ flux was 10 to 229% greater in the portable than in the static chamber at all measurement dates in all treatments. Average CO₂ flux across treatments and measurement dates was 9% lower in loam but 84% greater in sandy loam in the portable than in the static chamber. The CO₂ fluxes in the portable and static chambers were linearly to exponentially related (R² = 0.68 to 0.70, P ≤ 0.01, n = 40 to 56). Although the trends of CO₂ fluxes with treatments and measurement dates were similar in both methods, the flux varied with the methods in various soil types. Measurement of soil CO₂ flux by the portable chamber agreed more closely with the static chamber within 0-10 kg C ha^-1 d^-1 in loam soil under dryland than in sandy loam soil under irrigated and non-irrigated cropping systems.